The present invention relates to stabilized radiation detection systems and, more particularly, to a novel solid state radiation detector system utilizing negative feedback to establish the magnitude of an additional optical flux incident upon a detector element to maintain the charged particle and photon-induced electrical conductivity therein at a substantially constant value.
X-ray flux measurement systems, such as applicable to computerized transaxial tomography systems and the like, require X-ray detectors advantageously of great simplicity, ruggedness and compactness. A desirable radiation detector should utilize a solid state device for highly efficient detection and to alleviate the possibility of damage due to physical shock and movement. Such a simple solid state X-ray flux detector device may be fashioned from a bar of cadmium selenide activated with sodium (CdSe:Na). The conductance of a bar of sodium-doped cadmium selenide is of very low magnitude when the bar is shielded from incident flux; upon illumination of the bar with X-ray or optical (visible and near-infrared) light flux, the conductivity thereof increases. The change in conductivity of the solid state detector device may be measured to provide a measurement of the magnitude of the incident X-ray flux, although the change in conductivity has generally been found to be highly non-linear relative to changes in the incident X-ray flux and to exhibit undesirable changes in conductivity with time and temperature, whereby a relatively poor quality signal, i.e. the conductivity change responsive to change in incident X-ray flux renders the single solid state detector generally unusable in most medical X-ray systems.
It is desirable to provide a detector system not only capable of detecting ionizing radiation, e.g. gamma rays, X-rays charged particles, near-infrared and the like, but also capable of stabilizing a solid state detection element, whereby the high noise equivalent absorption of the solid state device (relative to a gaseous absorbing device), engendered by the relatively greater density of the detector material, may be fully realized. It is also desirable to provide simple circuitry to facilitate stabilization of the detector with a relatively compact physical structure whereby arrays of the detector systems become more practical for computerized transaxial tomography systems so that rapid, pseudo-real-time imaging of moving organs such as the human heart and the like, is facilitated.